2 replies to this topic

[rak_iam]

Hello there,

 

We have one debutanizer overhead cooler with sea water as cooling media on tube side. Supply & return headers are on ground level with supply pressure of 25 psig and return header is kept open to sea out side of refinery. Cooler is at elevated level of 5 mtrs above ground. Both supply and return piping are of 6 inch each. Supply and return headers are of 30 inch and 24 inch resp.

 

It is observe that vacuum being produced on return line of cooler at 7 inHg. When throttling the return valve to 80%, then only the positive pressure (1 psig) seen on gauge. We are facing low HT efficiency of cooler.

 

Is the vacuum creation because of cooler at above ground? or due to pressure loss on tube side? 28 psi loss on tube side can be expected?

 

Any thoughts and remedy?

 

Thanks in Advance.

[fallah]

Hi,

 

What can be extracted from the limited info you provided is that: 25 psig supply pressure isn't adequate to overcome the pressure loss in the system including frictional pressure loss in HX tube side and the main lines for required cooling water flow rate. Hence, you need to increase the supply pressure according the system hydraulic such that there would be a positive pressure at the return line outlet for the required flow rate.

[Zauberberg]

Pinching back on the outlet valve will actually increase cooling water flow, because this will suppress vacuum conditions. You only need to see by trial-and-error, or by hydraulic calculations, what is the optimum position of the valve.

 

With typically low pressures in the cooling water return header, exchanger outlet side can easily reach vacuum conditions if exchanger is at a sufficiently elevated point.